PROJECT SUMMARY/ ABSTRACT Interpersonal Psychotherapy (IPT) is a well-described and empirically validated treatment for depression. Though its efficacy is unassailable, it is often delivered with low fidelity in the community. We are in need of well-validated measures of fidelity to ensure that it is being delivered in the community at high quality so that patients benefit maximally. This proposal is submitted in response to NIMH RFA-MH-17-500, ?Pragmatic Strategies for Assessing Psychotherapy Quality in Practice.? The RFA specifically requests that proposals develop and test pragmatic strategies for evaluating psychotherapy fidelity that are both psychometrically rigorous and feasible for use in the community, and strongly emphasizes the need for large sample sizes so that the instruments and strategies are extremely well validated. Moreover, the RFA emphasizes the inclusion of all stakeholders in the process of instrument and strategy development. In response, we propose to conduct a two-phase study. Phase I will be a three year project to develop and validate 3 fidelity instruments (to be used by therapists, patients, and supervisors) as well as tools to abstract fidelity data from the medical record to measure the adherence and quality of the delivery of IPT. Specific steps include a review of qualitative feedback by IPT and other psychotherapy experts, community therapists, supervisors, administrators, and patients, with subsequent development of prototype measures of IPT effectiveness fidelity and tools to collect the data generated. These measures will then be pilot tested with 250 clinician-patient dyads in the community, comparing them to expert ratings of IPT and to standard outcome measures. The study will take place in the public mental health system in Los Angeles County, allowing us to work with an extremely diverse set of therapists and patients. We have done extensive work in LA, including training over 1300 therapists in IPT, developing an infrastructure to implement the treatment, and have established extensive liaison relationships with the LA County Department of Mental Health and 35 individual agencies within LA County. Phase II will be a prospective validation of our final instruments, which we will finalize using the data from our pilot trial and additional stakeholder and expert input. We will test the final instruments by comparing them to expert ratings of IPT and to standard outcome measures with another unique set of 250 therapist-patient dyads in the community. At the conclusion, we will collect data from all stakeholders to confirm feasibility and to estimate the cost of implementation and burden on the system. In sum, we will develop and test a well-validated system to measure of the fidelity of IPT treatment delivery and implementation in the community, including well-validated measures for use by therapists, supervisors, and patients.